First off, i wanted to say nice site. I've found it useful for alot of my problems. I've recently contacted Fyodor, and another nmap user about this issue. Of course, Fyodor is too busy to answer, and the other user hasnt been able to help with my situation. Here's the problem:Current OS: BackTrack 2 (Figured You'd Need This Info)Nmap Version: (Tried 4.20 Standard With BackTrack, Now Installed 4.22)I'm running scans on 50 hosts at a time, scanning the 4th Octet of the ip address. The Command I'm using is provided below:nmap -p 21,42,445,1433,1434,3389,5900 -P0 -T Insane xxx.xxx.xxx.1-50My issue is nmap is returning invalid results, its telling me all of the ports are open on each individual machine. Why is this? All help/suggestions are appreciated. Thank you in advanced.

Last edited by KrisTeason on Sat Sep 08, 2007 8:16 pm, edited 1 time in total.

maybe you can try throttling back on the sending of packets with the -T Insane to something a little slower. what kind of connection are you on? are you scanning outside of your subnet? what kind of network devices are between you and those hosts?

It's probably best to break your scan down and start with a single IP address. Does this produce the same results? If the ports are shown as open, can you use netcat to confirm this?

Running a port scan over a large address range can take time and it's very tempting to increase the scan rate. This is often not a good idea, I personally don't use anything higher then -T4, and I'll only use this on local addresses. Patience is important in doing a scan, if it's going to take a long time try running it overnight on a slower setting.